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Thursday, July 14, 2016

K40 Coolant Conductivity Matters!


After flailing for a few days with what I thought was a bad power supply or tube it dawned on me that I had never used distilled water (I am always tearing it apart and how conductive can the water be anyway?) and I knew that I had some algae in the tank.

I knew better from listening to others but seriously arching through the glass jacket through the water to ground in the tank? You better believe it, I have now proven it, to my satisfaction that is. I should have known better because I worked with someone that was blowing supplies every month and it turned out to be CAR antifreeze (that's definitely a no-no).

The symptoms was an intermittent screeching noise when the laser was in operation. It did not do it continuously and it did not do it every time. I thought it was coming from the LPS and finally was about to conclude that it was a failing winding inside the fly-back transformer. What bothered me was I could see no evidence of an arc even in a dark room. What I did notice was the flux beam shifting and changing shape at the anode end.

So I cleaned the system put in distilled water (3 Gal), powered it up and from then on no screeeeeeching just smooth wood smoking power. 

I wonder how many good supplies and tubes have been replaced or fry'd do to this problem.


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The Simplest Cooling System Approach

"The simplest and safest for humans and machines it to use pure distilled water in a closed system which prevents contaminates that might encourage algae growth. Change water every 6 months with other maintenance." 

From +Arthur Wolf 

The underlying principle is that pure uncontaminated distilled water does not grow algae.

Coolant Conductivity Data

Here is some actual data for cooling water conductivity. I don't know why I never thought of measuring this before. I wish I had measured the water before emptying it.
I used a HM Digital COM 100.
The temp was about 60F-65F
Distilled water = 2.6 uS
Distilled/RV mix:6:1 = 142 uS
RV antifreeze = 414 uS
Don's tap = 370 uS Prestone (ethelene glycol) = 633 uS
Vinegar: 137 uS
"Purified" water: 10uS
Aquarium algaecide: See below

uS = micro-siemens

Algaecide for Algae Prevention

Algaecide: Tetra Algea Control
Active ingredients: 5% Poly [Oxyethylene (Dimethyliminio) Ethylene (Dimethylimino)
Ethylene (Dimethylimino) Ethylene Dichoride]
Recommended dose for Aquariums: 1ml per 12 gallons, 1 drop (.084ml) per 1 gal (3.8L)
Conductivity measurements: 1 drop added to 1 gallon of fresh distilled water.
  • Reading before algaecide control = 4.8uS
  • Reading after adding algaecide = 4.9 uS
Conclusions: this brand of algae-cide does not raise the conductivity of distilled water. (continuing tests to be conducted).
Expectations: adding 5 drops, (.42ml) per 5 gallon bucket of distilled water will not increase the conductivity of the water but will prevent algae growth.

Clorox for Algae Prevention

Clorox: mostly sodium hypochlorite

Sodium Hypochlorite Conductivity (note: these measurements were made with an ohmmeter and that will not work so do not use this data). A meter will not work to measure conductivity because DC polarizes the solution. AC is used to solve this problem so insure your meter or measurement method uses AC.

Here is a better method for calculating.

Estimating Practical use of chlorine:

How much Clorox needed to kill algae?

1/4 teaspoon per gallon of water = .042 oz/gal
.042 * 5 = .21 oz/5 gal = 6.2 ml/5 gallons

Measurements to attain conductivity at relevant concentrations:

  1. 2.5 gallons distilled water was added to bucket. Conductivity = 2.2 uS
  2. Added 3 ml Clorox. Conductivity = 44.9 uS
  3. Added additional 2.5 gallons. Conductivity = 22 uS
  4. Added 3 ml Clorox. Conductivity = 46 uS

Final (for now) formula:

Mix 6 ml of Chlorox with 5 gallons of water and expect the conductivity to be in the 40's uS.

Long Term Testing of Water Conductivity

I started a test of tap water conductivity to see what the conductivity does over time and as algea grows. I am also monitoring my main tank (B).

Test setup:
A. Water in bucket: from my tap sitting indoors in open container
B.  Water in my K40 tank

My K40 tank (B) has the formula from above.

Tracking my water conductivity over time

Water bubble treatment

Clearing bubbles after a water replacement makes water replacement a chore as I have to lift (quite high) and rotate the machine to clear them.
If I could find a way to clear the bubbles I would be more motivated to change the water more often.

Rotate the tube:

I can do this but it will require an optical realignment and it increases the chances for HV arc to the case as the anode swings closer to the cabinet.

Add Water Wetter

I tried adding "Water Wetter" @ 1oz per 3 gallons. It raised the water conductivity from 4.0 us to 410us making the coolant unacceptably conductive. The bad part is that it did not remove the bubbles much at all.
Water Wetter measured without dilution is very conductive and read infinity on my meter. Even after I rinsed a bottle that had the wetter in it and then added distilled water it raised the conductivity from 4.0us to 40us.
The bottle suggests 1oz per gallon so I was using only 1/3 the amount recommended for car cooling systems.

Add Dish Detergent

I added 1/4 oz of Dawn to 3 gallons after the test above. It did not change the conductivity and it did not stop the bubbles.


Water as a Coolant for Lasers

Enjoy and comment,
Maker Don

1 comment:

  1. Exact same problem on my home built 40w system. I already ordered another tube thinking that was the problem, but a flush of my tap water and replacing it with distilled (with a little dish soap and algae preventer) and my power is back. In my case I seemed to lose power and hear the scream between around 8ma and 14ma. Its great at all power levels now!